View source for Electrothermal-chemical technology

{{Short description|Plasma ignition of projectile propellent}}
'''Electrothermal-chemical''' ('''ETC''') technology is an attempt to increase accuracy and muzzle energy of future [[tank]], [[artillery]], and [[close-in weapon system]]<ref>{{cite book | author1=Norman Friedman |author2=David K Brown |author3=Eric Grove |author4=Stuart Slade |author5=David Steigman | title=Navies in the Nuclear Age: Warships since 1945|publisher=Naval Institute Press|year=1993|page=163|isbn=1-55750-613-2}}</ref> guns by improving the predictability and rate of expansion of [[propellant]]s inside the barrel.

An electrothermal-chemical gun uses a plasma cartridge to ignite and control the ammunition's propellant, using electrical energy to trigger the process.  ETC increases the performance of conventional solid propellants, reduces the effect of temperature on propellant expansion and allows for more advanced, higher density propellants to be used.

The technology has been under development since the mid-1980s and in 1993 was actively being researched in the United States by the [[Army Research Laboratory]], [[Sandia National Laboratories]] and defense industry contractors, including [[FMC Corporation]], [[General Dynamics Land Systems]], [[Olin Corporation|Olin Ordnance]], and [[Soreq Nuclear Research Center]].<ref>Taulbee, Steve (1993). [https://babel.hathitrust.org/cgi/pt?id=uc1.c2979777;view=1up;seq=7 ARL Ballistics Research], U.S. Army Research Laboratory, p. 5.</ref>  It is possible that electrothermal-chemical gun propulsion will be an integral part of US Army's future combat system and those of other countries such as [[Germany]] and the [[United Kingdom]].  
Electrothermal-chemical technology is part of a broad research and development program that encompasses all electric gun technology, such as [[railgun]]s and [[coil gun]]s.

== Background ==
[[Image:XM360.png|right|thumb|The XM360.]]

The constant battle between [[vehicle armour|armour]] and armor-piercing round has led to continuous development of the main battle tank design. The evolution of American anti-tank weapons can be traced back to requirements to combat [[Soviet Union|Soviet]] tanks.  In the late 1980s, it was thought that the protection level of the Future Soviet Tank (FST) could exceed 700&nbsp;mm of rolled homogeneous armour equivalence at its maximum thickness, which was effectively immune against the contemporary [[M829]] [[kinetic energy penetrator|armour piercing fin stabilized discarding sabot]].<ref>Ropelewski, ''Soviet Gains in Armor/Antiarmor Shape US Army Master Plan'', p.69</ref>  In the 1980s the most immediate method available to NATO to counter Soviet advances in armour technology was the adoption of a 140&nbsp;mm main gun, but this required a redesigned turret that could incorporate the larger breech and ammunition, and it also required some sort of automatic loader.<ref>Schemmer, ''Army, SecDef's Office at Loggerheads over Antiarmor'', p.53</ref> Although the 140&nbsp;mm gun was considered a real interim solution it was decided after the fall of the Soviet Union that the increase in muzzle energy it provided was not worth the increase in weight. Resources were therefore spent on research into other programs that could provide the needed muzzle energy. One of the most successful alternative technologies remains electrothermal-chemical ignition.

Most proposed advances in gun technology are based on the assumption that the solid propellant as a stand-alone propulsion system is no longer capable of delivering the required muzzle energy.  This requirement has been underscored by the appearance of the Russian [[T-90]] main battle tank.  The elongation of current gun tubes, such as the new German 120&nbsp;mm L/55,<ref>The length of the cannon can be found by multiplying the diameter of the barrel and the caliber length.  For example, the M256, which is a 120 mm L/44, has a total length of 5.28 m, while the 120 mm L/55 has a total length of 6.6 m.</ref> which was introduced by Rheinmetall is considered only an interim solution as it does not offer the required increase in muzzle velocity.<ref>Sharoni, ''The Future Combat System'', p. 29</ref>  Even advanced kinetic energy ammunition such as the United States' [[M829A3]] is considered only an interim solution against future threats.<ref>Pengelley, ''The new era in tank main armament'', p.1522</ref> To that extent the solid propellant is considered to have reached the end of its usefulness, although it will remain the principal propulsion method for at least the next decade{{clarify|date=July 2015}} until newer technologies mature.<ref>Sharoni, ''The Future Combat System'', p.30</ref>  To improve on the capabilities of a solid propellant weapon the electrothermal-chemical gun may see production as early as 2016.<ref>Kruse, ''Studies on Germany's Future 140 mm Tank Gun System'', p. 1</ref>{{update inline|date=February 2022}}

ETC technology offers a medium-risk upgrade and is developed to the point that further improvements are so minor that it can be considered mature.{{citation needed|date=July 2015}}  The lightweight American 120&nbsp;mm [[XM291]] came close to achieving 17 MJ of muzzle energy, which is the lower-end muzzle energy spectrum for a 140&nbsp;mm gun.<ref>Diamond, ''Electro Thermal Chemical Gun Technology Study'', p.5</ref>  However, the success of the XM291 does not imply the success of ETC technology as there are key parts of the propulsion system that are not yet understood or fully developed, such as the plasma ignition process.  Nevertheless, there is substantial existing evidence that ETC technology is viable and worth the money to continue development.  Furthermore, it can be integrated into current gun systems.<ref>Sauerwein, ''Rheinmetall's NPzK''</ref>

== Operational Principle ==
[[Image:ETC.png|right|thumb|upright=1.35|A diagram of a working electrothermal-chemical gun.]]

An electrothermal-chemical gun uses a plasma cartridge to ignite and control the ammunition's propellant, using electrical energy as a catalyst to begin the process.  Originally researched by Dr. Jon Parmentola for the U.S. Army, it has grown into a very plausible successor to a standard solid propellant tank gun.  Since the beginning of research the United States has funded the XM291 gun project with USD 4,000,000, basic research with USD 300,000, and applied research with USD 600,000.{{Citation needed|date=August 2008}}  Since then it has been proven to work, although efficiency to the level required has not yet been accomplished.  ETC increases the performance of conventional solid propellants, reduces the effect of temperature on propellant expansion and allows for more advanced, higher density propellants to be used.  It will also reduce pressure placed on the barrel in comparison to alternative technologies that offer the same muzzle energy given the fact that it helps spread the propellant's gas much more smoothly during ignition.<ref>Hilmes, ''Aspects of future MBT conception''</ref>  Currently, there are two principal methods of plasma initiation: the flashboard large area emitter (FLARE) and the triple coaxial plasma igniter (TCPI).

=== Flashboard large area emitter ===
Flashboards run in several parallel strings to provide a large area of plasma or ultraviolet radiation and uses the breakdown and vaporization of gaps of diamonds to produce the required plasma.  These parallel strings are mounted in tubes and oriented to have their gaps azimuthal to the tube's axis. It discharges by using high pressure air to move air out of the way.<ref>Diamond, ''Electro Thermal Chemical Gun Technology Study'', pp.11-12</ref>  FLARE initiators can ignite propellants through the release of plasma, or even through the use of ultraviolet heat radiation.<ref>Diamond, ''Electro Thermal Chemical Gun Technology Study'', pp.13-15</ref>   The absorption length of a solid propellant is sufficient to be ignited by radiation from a plasma source.  However, FLARE has most likely not reached optimal design requirements and further understanding of FLARE and how it works is completely necessary to ensure the evolution of the technology.  If FLARE provided the XM291 gun project with the sufficient radiative heat to ignite the propellant to achieve a muzzle energy of 17 MJ one could only imagine the possibilities with a fully developed FLARE plasma igniter.  Current areas of study include how plasma will affect the propellant through radiation, the deliverance of mechanical energy and heat directly and by driving gas flow.  Despite these daunting tasks FLARE has been seen as the most plausible igniter for future application on ETC guns.<ref>For further technical information on FLARE ''see:'' P. Diamond</ref>

=== Triple coaxial plasma igniter ===
A coaxial igniter consists of a fully insulated conductor, covered by four strips of aluminium foil.  All of this is further insulated in a tube about 1.6&nbsp;cm in diameter that is perforated with small holes.  The idea is to use an electrical flow through the conductor and then exploding the flow into vapour and then breaking it down into plasma.  Consequently, the plasma escapes through the constant perforations throughout the insulating tube and initiates the surrounding propellant.  A TCPI igniter is fitted in individual propellant cases for each round of ammunition.  However, TCPI is no longer considered a viable method of propellant ignition because it may damage the fins and does not deliver energy as efficiently as a FLARE igniter.<ref>TCPI is also covered in ''Electro Thermal Chemical Gun Technology Study'' by P. Diamond</ref>

== Feasibility ==
[[Image:60mmETC.PNG|right|thumb|upright=1.35|The 60 mm ETC gun developed by the US Navy at FMC as an ETC CIWS proof of principle demonstrator.]]

The XM291 is the best existing example of a working electrothermal-chemical gun.  It was an alternative technology to the heavier caliber 140&nbsp;mm gun by using the dual-caliber approach.  It uses a breech that is large enough to accept 140&nbsp;mm ammunition and be mounted with both a 120&nbsp;mm barrel and a 135&nbsp;mm or 140&nbsp;mm barrel.  The XM291 also mounts a larger gun tube and a larger ignition chamber than the existing M256 L/44 main gun.<ref>Pengelley, ''A new era in tank main armament'', p. 1522</ref>  Through the application of electrothermal-chemical technology the XM291 has been able to achieve muzzle energy outputs that equate that to a low-level 140&nbsp;mm gun, while achieving muzzle velocities greater than those of the larger 140&nbsp;mm gun.<ref>Sharoni, ''The Future Combat System'', p.31</ref>  Although the XM291 does not mean that ETC technology is viable it does offer an example that it is possible.

ETC is also a more viable option than other alternatives by definition. ETC requires much less energy input from outside sources, like a battery, than a [[railgun]] or a [[coilgun]] would.  Tests have shown that energy output by the propellant is higher than energy input from outside sources on ETC guns.<ref> Diamond, ''Electro Thermal Chemical Gun Technology Study'', {{pn|date=December 2023}}</ref>  In comparison, a railgun currently cannot achieve a higher muzzle velocity than the amount of energy input.  Even at 50% efficiency a rail gun launching a projectile with a kinetic energy of 20 MJ would require an energy input into the rails of 40 MJ, and 50% efficiency has not yet been achieved.<ref>Horst, ''Recent Advances in Anti-Armor Technology'', p.6</ref>  To put this into perspective, a rail gun launching at 9 MJ of energy would need roughly 32 MJ worth of energy from capacitors.  Current advances in energy storage allow for energy densities as high as 2.5 MJ/dm³, which means that a battery delivering 32 MJ of energy would require a volume of 12.8 dm³ per shot; this is not a viable volume for use in a modern main battle tank, especially one designed to be lighter than existing models.<ref>Zahn, ''The Future Combat System: Minimizing Risk While Maximizing Capability'', p.20</ref>  There has even been discussion about eliminating the necessity for an outside electrical source in ETC ignition by initiating the plasma cartridge through a small explosive force.<ref>Yangmeng, ''A Novel Concept of Electrothermal Chemical Gun without Power Supply'', p.1</ref>

Furthermore, ETC technology is not only applicable to solid propellants.  To increase muzzle velocity even further electrothermal-chemical ignition can work with liquid propellants, although this would require further research into plasma ignition.  ETC technology is also compatible with existing projects to reduce the amount of recoil delivered to the vehicle while firing.  Understandably, recoil of a gun firing a projectile at 17 MJ or more will increase directly with the increase in muzzle energy in accordance to [[Newton's laws of motion|Newton's third law of motion]] and successful implementation of recoil reduction mechanisms will be vital to the installation of an ETC powered gun in an existing vehicle design.  For example, [[OTO Melara]]'s new lightweight 120&nbsp;mm L/45 gun has achieved a recoil force of 25 t by using a longer recoil mechanism (550&nbsp;mm) and a pepperpot muzzle brake.<ref>Hilmes, ''Arming Future MBTs'', p.79</ref>  Reduction in recoil can also be achieved through mass attenuation of the thermal sleeve.  The ability of ETC technology to be applied to existing gun designs means that for future gun upgrades there's no longer the necessity to redesign the turret to include a larger breech or caliber gun barrel.

Several countries have already determined that ETC technology is viable for the future and have funded indigenous projects considerably.  These include the United States, Germany<ref>Hilmes, ''Modern German Tank Development'', pp.20-21.</ref> and the United Kingdom, amongst others.  The United States' [[XM360]], which was planned to equip the [[Future Combat Systems]] [[Mounted Combat System]] light tank and may be the [[M1 Abrams]]' next gun upgrade, is reportedly based on the XM291 and may include ETC technology, or portions of ETC technology. Tests of this gun have been performed using "precision ignition" technology, which may refer to ETC ignition.

== Notes ==
{{reflist|30em}}

== Bibliography ==
{{refbegin|30em}}
* {{cite report
  | last = Diamond
  | first = P.
  | title = Electro Thermal Chemical Gun Technology Study
  | publisher = The MITRE Corporation
  | date = March 1999
  | citeseerx = 10.1.1.834.5851
  }}
* {{cite journal
  | last = Hilmes
  | first = Rolf
  | title = Arming Future MBTs - Some Considerations
  | journal = Military Technology
  | issue = 12/2004
  | publisher = Moench Verlagsgesellschaft Mbh
  |date=December 2004
  }}
* {{cite journal
  | last = Hilmes
  | first = Rolf
  | title = Aspects of future MBT conception
  | journal = Military Technology
  | volume = 23
  | issue = 6
  | publisher = Moench Verlagsgesellschaft Mbh
  | date = June 30, 1999
  }}
* {{cite journal
  | last = Hilmes
  | first = Rolf
  | title = Battle Tanks for the Bundeswehr: Modern German Tank Development, 1956-2000
  | journal = Armor
  | issue = January–February 2001
  | publisher = Fort Knox: US Army Armor Center
  | date = January 1, 2001
  | issn = 0004-2420  }}
* {{cite conference
  | last= Horst
  | first = Albert W. 
  | title = Recent advances in anti-armor technology
|book-title=35th Aerospace Sciences Meeting and Exhibit
  | publisher = American Institute of Aeronautics and Astronautics
  | year = 1997
  |display-authors=etal
|doi=10.2514/6.1997-484}}
* {{cite conference
  | last= Kruse
  | first = Josef
|display-authors=etal
|url=https://id3486.securedata.net/fprado/armorsite/Leo2_Files/tanks.140mm-gun.kruse.pdf
  | title = Studies on Germany´s Future 140 mm Tank Gun Systems - Conventional and ETC -
|book-title=34TH Gun & Ammunition Symposium & Exhibition
  | publisher = Rheinmetall
  | date = April 1999
|via=The Armor Site
  }}
* {{cite journal
  | last = Ogorkiewicz
  | first = Richard M.
  | title = Future tank guns Part I: solid and liquid propellant guns
  | journal = International Defense Review
  | issue = 12/1990
  | publisher = Janes
  |date=December 1990
  }}
* {{cite journal
  | last = Pengelley
  | first = Rupert
  | title = A new era in tank main armament: The options multiply
  | journal = International Defense Review
  | issue = 11/1989
  | publisher = Janes
  |date=November 1989
  }}
* {{cite journal
  | last = Ropelewski
  | first = Robert R.
  | title = Soviet Gains in Armor/Antiarmor Shape US Army Master Plan
  | journal = Armed Forces Journal International
  | publisher = U.S. Army
  |date=February 1989
  }}
* {{cite journal
  | last = Schemmer
  | first = Benjamin F.
  | title = Army, SecDef's Office at Loggerheads over Antiarmor
  | journal = [[Armed Forces Journal International]]
  | publisher = U.S. Army
  |date=May 1989
  }}
* {{cite journal
 |last       = Sharoni
 |first      = Asher H.
 |author2    = Lawrence D. Bacon
 |url        = https://www.knox.army.mil/center/ocoa/armormag/backissues/1990s/1997/so97/5fcs97.pdf
 |title      = The Future Combat System (FCS): Technology Evolution Review and Feasibility Assessment
 |journal    = Armor
 |publisher  = Fort Knox: US Army Armor Center
 |date       = September 1, 1997
 |issn       = 0004-2420
}} {{Dead link|date=January 2019 |bot=InternetArchiveBot |fix-attempted=yes }}
* {{cite journal
  | last = Sauerwein
  | first = Brigitte
  | title = Rheinmetall's NPzK: Conventional technology for counterng future MBTs
  | journal = International Defense Review
  | issue = 2/1990
  | publisher = Janes
  |date=February 1990
  }}
* {{cite book
  | last= Yangmeng
  | first = Tian
  | title = A Novel Concept of Electrothermal Chemical Gun without Power Supply
  |display-authors=etal}}
* {{cite report
  | last = Zahn
  | first = Brian R.
  | title = The Future Combat System: Minimizing Risk While Maximizing Capability
|url=https://apps.dtic.mil/sti/citations/ADA574181
|website=Defense Technical Information Center
  | date = May 2000
  }}
{{refend}}

== External links ==
* [https://web.archive.org/web/20060623132304/http://www.emlsymposium.org/ Electromagnetic Launch Symposium]
* http://www.powerlabs.org/electrothermal.htm

[[Category:Artillery by type]]
[[Category:Propellants]]
[[Category:History of the tank]]